Communication devices such as User Equipments (UE) are also known as e.g. mobile terminals, wireless terminals and/or mobile stations. User equipments are enabled to communicate wirelessly in a cellular communications network or wireless communication system, sometimes also referred to as a cellular radio system or a cellular network. The communication may be performed e.g. between two user equipments, between a user equipment and a regular telephone and/or between a user equipment and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the cellular communications network.
User equipments may further be referred to as mobile telephones, cellular telephones, laptops, or surf plates with wireless capability, just to mention some further examples. The user equipments in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another user equipment or a server.
The cellular communications network covers a geographical area which is divided into cell areas, wherein each cell area is served by a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. “eNB”, “eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the user equipments within range of the base stations. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the user equipment. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the user equipment to the base station.
In some RANs, several base stations may be connected, e.g. by landlines or microwave, to a radio network controller, e.g. a Radio Network Controller (RNC) in Universal Mobile Telecommunications System (UMTS), and/or to each other. The radio network controller, also sometimes termed a Base Station Controller (BSC) e.g. in GSM, may supervise and coordinate various activities of the plural base stations connected thereto. GSM is an abbreviation for Global System for Mobile Communications (originally: Groupe Spécial Mobile).
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
3GPP LTE radio access standard has been written in order to support high bitrates and low latency both for uplink and downlink traffic. All data transmission is in LTE controlled by the radio base station.
The extensive growth in the number of users and service usage time contributes an increasing demand for energy consumption in the field of cellular networks. To reduce the energy consumption in cellular networks is desirable which would not only minimize the environmental impact on climate change, but also reduce the operational expenses. The RBS contribute a significant portion of the whole network energy consumption. Therefore, it will be very valuable if the energy consumption of the RBS can be greatly reduced.
In order to solve this problem, several power saving schemes have recently been proposed on RBS. One way is to use more energy efficient BS hardware, or using site solutions to reduce the energy consumption of BS, such as efficient cooling systems, etc.
Another way is related to system level features, to balance between energy consumption and performance, aiming at intelligent control of the network elements. Furthermore, the renewable sources may be used to power RBS, especially solar or wind power or a combination of both.
Among the system level features, the main concept is to continuously detect the traffic load in a certain area. The traffic load in cellular networks varies greatly from time to time. Because the current radio systems are always optimized for maximum load, a large amount of energy will be wasted when the real traffic load is small. Therefore, when the traffic load is low, the current cell may be switched off or turned into sleep mode. The network traffic may be assumed to vary due to two effects: typical day-night behaviour of users and the daily swarming of users carrying their user equipments from residential areas to office districts and back. In “M. A. Marsan, L. Chiaraviglio, D. Ciullo and Mi. Meo, Optimal Energy Savings in Cellular Access Networks, Proc. IEEE ICC '09 Workshop, GreenComm, 2009”, a simple analytical model for energy saving and energy-aware management of cellular access networks is disclosed. It saves energy by reducing the number of active cells during the periods when they are not necessary because traffic is low. When some cells are switched off, radio coverage is taken care of by the cells that remain active, so as to guarantee that service is available over the whole area. The simulation shows that energy savings of the order of 25-30% are possible. The main disadvantage of this solution is that the traffic is assumed in a very simplified way. Thus, the targets are assumed to be fixed, and the time variation of the “traffic” is not explored.
Moreover, distance between base station and the user equipment may be used for efficient sector power control. In “Document S. Hwan Lee, Y. Choi, S. Park, S. Hyong Rhee, An energy efficient power control mechanism for base stations in mobile communication systems, Proceedings of Information Networking (ICOIN), 2011” an energy efficient power control mechanism for base station in mobile communication systems is provided. Further, an efficient sector power control based on distance between base station and mobile node is disclosed. Also a sleep mode energy control mechanism is provided. In a sleep mode energy saving protocol, each sector monitors the number of user equipments in a sector cell. If the number of user equipments falls below a given threshold in the sector cell, the base station shuts down its power. Simulation demonstrate that the transmitting energy may be saved by proposed algorithms, and there is a trade-off between energy saving and cell coverage.
When some cells are turned off, the reliable coverage and service provisioning is worsened.